Approximately 1 in 3 persons with diabetes are nonadherent to their medications. Nonadherence is more common among low income, racial/ethnic minorities with type 2 diabetes (T2DM), and is a strong, independent predictor of poor glycemic control, hospitalizations, mortality, and higher healthcare costs. Theory-based adherence promotion interventions are more effective than atheoretical, ad hoc approaches, and are needed for patients at highest risk of nonadherence. A well-validated theoretical model, the Information-Motivation-Behavioral Skills (IMB) model, has informed effective medication adherence promotion interventions for patients with HIV and hypertension, and should inform adherence interventions in diabetes. Moreover, widely available technologies, such as mobile phones, offer a means to deliver adherence interventions to a broad range of patients, including low income, racial/ethnic minorities at high risk of nonadherence. The goal of this research is to use the IMB model to inform the content and functionality of a mobile phone- delivered medication adherence promotion intervention, ensure intervention content is clearly communicated (i.e., uses simplified text and plain language), and evaluate intervention effects on adherence and glycemic control among a low income adults with T2DM receiving primary care at Federally Qualified Health Centers (FQHCs). The Specific Aims and Research Strategy include: (1) improving the content and functionality of an existing mobile phone-delivered medication adherence promotion to be consistent with the IMB model and clear health communication strategies, and testing for usability and acceptability with 36 patients before evaluating the intervention's effect on outcomes; (2) performing a randomized controlled trial with 500 patients at two FQHCs to test the effect of the intervention on subjective and objective measures of medication adherence, other self-care behaviors and glycemic control at 3, 6, 12, and 15 months, and test whether the IMB mechanisms mediate intervention effects on adherence, test whether adherence mediates intervention effects on glycemic control, and test whether health literacy, numeracy, depression, and/or insulin status moderate intervention effects; and (3) develop recommendations for implementing and evaluating mobile phone-delivered interventions for low-income patients by conducting focus groups with intervention patients and clinic staff to identify the contextual influences on acceptance and effectiveness of the intervention. This interdisciplinary research will greatly enhance our understanding of how to address social-cognitive barriers to adherence among high-risk patients with diabetes, how to leverage mobile devices to support high- risk patient populations in general; and how to better design interventions to improve services for low income, racially/ethnically diverse patients, as well as other high-risk groups. Knowledge gained form this work may also inform interventions to reduce disparities in adherence, glycemic control, and other diabetes outcomes.